Reed switch control



Nov. 2, 1965 I H. MATTHIAS 3,215,795

REED SWITCH CONTROL Filed Jan. 3, 1963 2 Sheets-Sheet 1 NI COIL l2 HINVENTOR LYNN H. MATTHIAS ATTORNEY Nov. 2, 1965 H. MATTHlAS 3,215,795

REED SWITCH CONTROL Filed Jan. 3, 19 3 2 Sheets-Sheet 2 INVENTOR LYNN H.MATTHIAS New ATTORNEY United States Patent 3,215,795 REED SWITCH CONTROLLynn H. Matthias, Fox Point, Wis., assignor to Allen- Brarlley Company,Milwaukee, Wis., a corporation of Wisconsin Filed Jan. 3, 1963, Ser. No.249,185 3 Claims. (Cl. 20087) This invention relates to reed switchcontrols and it more specifically resides in a reed switch having twomagnetic reeds with relatively movable contact ends, a magnetic memberdisposed adjacent the contact ends to modify magnetic field patternsassociated with the reeds, and operating coils located on both sides ofthe magnetic member which function to close the reed contacts when bothcoils are energized.

Reed switches comprise a pair of thin, magnetic reeds within a glassenvelope. At least one of the reeds is deflectable, and the ends of thereeds overlap slightly to function as switch contacts that move betweenopen and closed positions in response to associated operating coils orother energizing means. These switches are particularly useful incircuits utilizing numerous switching elements that must operate with avery high degree of reliability over an extended time, and they arecharacterized by a rapid switching operation that makes them ideal forcomputer devices, logic circuits and telephone circuits.

In a host of reed switch applications the switch is combined with a pairof operating coils, and the reed contacts are to close only whensimultaneous independent signals are transmitted to such associatedcoils. Cross-point switching is a typical application of this nature. Insome other applications the reed switch must also return its contacts toopen position upon discontinuance of either of the signals. It thenfunctions as an and logic circuit element for both energization anddeenergization of the operating coils.

In usual construction employing a pair of operating coils, each coilencircles one of the reeds and when it is energized by a current ofprescribed value it develops a magnetic flux insuflicient to close theswitch. However, upon energization of both coils the resultant fiux inthe vicinity of the reed contact ends closes the switch, and in theinstance of an an type switch deenergization of a single coil will causethe switch to reopen. Such a device may have limited magnetic tolerancesfor proper operation, with the result that either excessive or deficientamounts of flux may be developed if any construction or operatingparameter is altered to any considerable degree. For example, when themagnetizing force of each individual coil is small enough to be belowthe drop out (switch opening) value, the combined magnetizing forcesobtained upon simultaneous energization of the coils may not be muchgreater than the minimum at which switch closing will occur. In suchswitches a decrease in the applied voltages may result in the switch notclosing when both coils are energized, and also the switch may remainclosed when one coil is de-energized if the operating voltage isslightly increased. Also, if there is a small dilference between themagnetizing force required to pick up the switch and the magnetizingforce required to drop out the switch, then a relatively small increasein voltage applied to a single coil may cause switch closure. Thus, somereed switch controls have serious disadvantages.

The present invention comprises a control for a reed switch having amain operating coil for each reed in combination with a magnetic memberdisposed in the immediate vicinity of the reed contact ends at aposition between the coils. This magnetic member modifies the magneticfield in the vicinity of the contact ends to insure retention of thereeds in their initial open position upon Patented Nov. 2, 1965energization of only one of the main operating coils. This retention ismaintained for large values of magnetizing ampere turns being appliedthrough the single coil, so that applied voltages can increase withoutaffecting the characteristic of retaining the switch open until signalsare applied to both coils. Thus, only upon energization of both coilswill the reed contacts be actuated to closed position. The presence ofthe magnetic member also improves switch opening characteristics, inthat the applied voltage to the coils does not have to be as criticallycontrolled in order to have switch opening occur when one coil is deenergized. To further enhance a rapid, positive reopening of the reedcontacts a supplementary reverse coil may be used with each main coil toreduce the magnetic potential between the reed contacts upondeenergization of either main coil. Then, extreme reliability isobtained for operation as anand logic circuit element.

It is an object of this invention to provine a reed switch control whichwill operate over a large range of line voltages without impairing theoperating characteristics of the switch assembly.

It is another object of this invention to provide a reed switch assemblyin which magnetic interaction between closely adjacent switches isreduced to levels wherein adjacent switches do not influence oneanother, so that a compact assembly of a plurality of reed switches maybe obtained.

It is another object of this invention to provide a reed switch controlwhich is characterized by reliable operation, and which is nothandicapped by severely critical switch response characteristics.

I It is another object of this invention to provide a reed switchcontrol that may be readily manufactured in large numbers withsubstantial manufacturing tolerances.

The foregoing and other objects and advantages of this invention willappear from the description to follow. In the description reference ismade to the accompanying drawings which form'a part hereof, and in whichthere are shown by way of illustration, and not of limitation, specificembodiments in which the invention may reside. For a determination ofthe scope of the invention, as distinguished from the specificness ofthe embodiments illustrated, reference is made to the claims appendedhereto.

In the drawings:

FIG. 1 is a view of a reed switch control embodying the invention with amagnetic flux diverting plate broken away and in section and withoperating coils depicted schematically,

FIG. 2 is a graph of characteristics of the reed-switch of FIG. 1,

FIG. 3 is a view of a reed switch like that in FIG. 1 modified by theaddition of permanently magnetized latching magnets,

FIG. 4 is a view of another reed switch control embodying the invention,and

FIG. 5 is a side view, with parts in section, of an assembly of a numberof reed switch controls of the invention.

Referring now to the drawings, there is shown in FIG. 1 a sealed, glassenvelope 1 preferably filled with an inert gas. A pair of long, thinreeds 2 and 3 extend into the interior of the envelope 1 from itsopposite ends 4 and 5. The reeds 2, 3 are of a magnetic material thathas suflicient flexnre to provide for movement of the inner ends 6, 7 atthe center of the envelope 1. The inner ends 6, 7 are normally open andthey overlap slightly to present facing contact surfaces that will moveinto engagement with one another in response to magnetic forcesestablished by associated coils. The reeds 2 and 3 also have suflicientconducting qualities to form satisfactory switch elements for anelectric circuit, and thin external ends 8 and 9 function as terminalsfor connection into such a circuit. In the usual manufacture of thesedevices, the reeds 2, 3 have a diffused gold coating that insures longand stable electrical life, and by providing an inert gas filledenvelope 1, contact failure due to dust, dirt or atmosphericcontamination is virtually eliminated. The glass envelope 1 with itsreeds 2, 3 comprises what is known as a reed switch, and, as stated, isuseful in telephone circuits, computer elements such as decoders andshift registers, and similar apparatus where reliable high speedswitching is essential.

The glass envelope 1 extends through a close fitting opening of amagnetic plate 11 that is centered with respect to the contact ends 6and 7. A first operating coil 12 encircles the left hand end of theenvelope 1, as viewed in FIG. 1, and its ends are joined to a pair ofterminals 13 and 14. A second operating coil 15 encircles the right handend of the envelope 1 and has one end 'joined to the common terminal 13while its other end extends to a terminal 16. Thus, the two coils 12, 15can be independently energized, and if desired they can have entirelyseparate terminals instead of a common connection such as the terminal13.

In the operation of the device of FIG. 1, the presence 'of the magneticplate 11 provides a mode of operation distinctly diiferent from thatheretofore had in the absence of such member. If either coil 12 or 15 isenergized, without any energization of the other, the contact ends 6, 7will remain open, and this open condition will persist for large valuesof ampere-turns well above normal operating values. By properproportioning of the magnetic plate 11 the range may extend to currentvalues causing a destruction of the coil, so that switch closure isdefinitely precluded. As a consequence an unwanted closing of thecontact ends 6, 7 will not occur upon energization of but a single coil12, or 15, and fluctuations in operating voltage will not alter thisswitching characteristic. The plate 11 influences the pattern of themagnetic field in the vicinity of the contact ends 6, 7 to maintain alow value of flux density between the reed ends 6, 7 that isinsufficient to develop a closing force between the reeds.

For the condition of a single energized coil, for example coil 12, asubstantial amount of the magnetic flux in the right hand end of theassociated reed 2 will be shunted off toward the plate 11 to inhibit thepassage of any critically suificient amount of flux from reed end 6 toreed end 7 that would close the contacts. Flux shunted to, or divertedby, the plate 11 will pass from the plate 11 about the outside of thecoil 12 to link therewith, and since it is primarily an air flux thatdoes not give rise to a closing force for the contact ends 6, 7 it canbe termed a leakage flux.

The coils 12 and 15 are connected to have their respective magnetic fluxcomponents in the reeds 2, 3 add to one another. Thus, for conventionalsymbolic representation applied to FIG. 1, when a positive voltagesignal is simultaneously applied to the terminals 14 and 16 the magneticflux through the center of each coil 12, 15 will be from the right tothe left, and the cumulative eifects at the reed contacts 6, 7 willproduce a sufficient magnetic intensity across the open contact gap tomove the contact ends into closed position. Thus, switch closure is onlyestablished by simultaneous coil energization, and by virtue of the fluxdiverting plate 11, the unique switch characteristic shown in FIG. 2 isobtained.

In FIG. 2 the abscissa of the graph represents ampereturns for the coil12 and the ordinate represents ampereturns for the coil 15. The curve 17is a plot of limiting values of ampere-turns for the two coils 12, 15for which switch closure is obtained, and this curve is substantiallyasymptotic so that there is some threshold value of ampere-turns foreach coil that is required for switch closure, even though a very highvalue of ampere-turns is applied through the other coil. This thresholdvalue is represented by the letter m in FIG. 2. If the two coils 12, 15are operated with equal ampere-turns switch operation will be along theline 18, and the point 19 is the minimum value of equal ampere-turns atwhich switch closure occurs. It is advantageous to have a locus for thepoint 19 that requires only small ampere-turn values for the two coils,and by proper dimensioning of the diverter plate 11 and positioning ofthe coils 12, 15 the coordinates x and y for the point 19 can each bebrought within two times the necessary minimum ampere-turns m requiredfor either coil for switch closure.

The arrangement of FIG. 1 can be modified by the inclusion of latchingmagnets at each side of the diverter plate 11, as shown in FIG. 3, wherea set of four small permanent magnets 20 are disposed and oriented todevelop a small biasing flux that passes through the reeds 2, 3 in thesame direction as that developed by the coils 12, 15. (Like referencenumerals have been applied in FIG. 3 for parts that correspond withparts in FIG. 1.) By this arrangement the reeds 2, 3 can be closed byapplying simultaneous signal pulses to the coils 12, 15 and the latchingmagnets 20 will then hold the reeds closed. To open the reeds a reverseclearing pulse can be applied to either coil 12 or 15. The magnetic fluxat the reed contact ends due to the permanent magnets 20 may be of sucha value that the switch can be closed by applying a large number ofampere-turns through a single coil. However, the ampere-turns that wouldbe required may greatly eX- ceed the ampere-turns required per coil whenclosing by simultaneous energization of both coils with equalampore-turns for each. In actual practice, the ratio of the ampere-turnsrequired for switch closure by a single coil to the ampere-turns percoil when closed by simultaneous energization has been as great as 4:1and more. These results have been obtained for a reed switch 0.2 inch indiameter and with a magnetic flux diverting member A inch thick.

Referring now to FIG. 4, there is shown a reed relay comprised of aglass envelope 1 and reeds 2 and 3. (Like reference numerals have againbeen applied to parts like those shown in FIG. 1.) Associated with thisrelay is a magnetic flux diverting plate 11 and a group of operatingcoils which differ from those in FIG. 1 by the inclusion ofsupplementary coils that are connected to have reverse turns forestablishing magnetic flux components in opposition that-of the maincoils. Thus, there is a first coil set comprising a main operating coil21 encircling the left hand side of the envelope 1 and a supplementarycoil 22 on the opposite side of the diverting plate 11 that encirclesthe right hand side of the envelope 1. One end of the main coil 21 isconnected to a common terminal 23, shown as a negative terminal, and theopposite end of the main coil 21 is connected through a lead 24 to thesupplementary coil 22 in a manner to have the respective coil windingsin opposition to one another. The supplementary coil 22 has fewer turnsthan the main coil 21, and upon energization the magnetic fields due tothe common current flowing in the two coil sections 21, 22 will be inopposition to one another, with the field of the larger coil 21 beingthe larger. But, similarly as for the device of FIG. 1, the reed switchwill remain open even though large currents be caused to flow throughthe first coil set, so that a characteristic curve is obtained which issimilar to that in FIG. 2.

A second coil set comprises a main operating coil 25 encircling theright hand side of the envelope 1 and a second supplementary coil 26 onthe opposite side of the magnetic plate 11. A lead 27 extends from oneend of the coil 25 to a common connection with the coil 21, and anotherlead 28 joins the opposite end of the coil 25 with the supplementarycoil 26. The winding relation between the second main coil 25 and thesecond supplementary coil 26 is like that of the first coils 21, 22, inthat the turns of the supplementary coil 26 are of lesser number and inopposition to the turns of the main coil 25. The coils are furtherarranged so that the main coils 21, 25 have their .fields add tooneanother.

.set the reed switch will open.

, h In operating the reed switch of FIG. 4 both the first .and secondset of coils must be operated to close the reed contacts, and upondeenergization of either set of coils 21, 22 or 25, 26 the contacts willreopen. Thus, for

example, if the first set of coil sections 21, 22 be energized .withterminal 23 negative, the magnetic flux established This retention ofopen contact position results from the presence of the magnetic plate11, and .as in FIG. 1 the pattern. of the magnetic field in the vicinityof the reed contact ends is modified by the presence of the surroundingmagnetic plate 11 to prohibit the value for the magnetic flux betweenreeds 2 and 3 from developing a force between the reeds sufiicient toclose the switch.

. Upon energizing the second coil set, the reeds 2, 3 will close. Themagnetic flux of the second main coil 25 established in the right handreed 3 is cumulative to that of the first main coil 21, so that for theflux path extending from reed 2 to reed 3, the magnetic intensitybetween reeds 2, 3 is sharply increased and an attractive forcesufiicient to close the reed contact ends 6, 7 is attained.

Now, upon deenergizing either the first or second coil The reversedsupplementary coil which remains energized, such as the coil 22 in theevent the second set of coils 25, 26 are deenergized, will cause agreater reduction in the magnetic forces between the closed relaycontacts to ensure an .operation.

An example of the use of several reed switches with one flux divertingmagnetic plate is shown in FIG. 5. A

mounting block 30 which may also serve as a terminal block, supports apair of non-magnetic shafts 31 and 32.

The shafts 31, 32 are each threaded at one end to support a magneticplate 33, which functions as the plate 11 of FIGS. 1, 3 and 4. A groupof three glass enveloped reed switches are inserted in appropriateopenings in the magnetic plate 33, and parts of the middle assembly arebroken away to show one of these switches 34. Coil assemblies 35 and 36are placed over the reed switch '34, one oneach side of theplate 33. Theparticular coil assembl'ies.,35.and 36 have .coil sets, similarly as inFIG. 4, and for thecoilassembly 35 .a main operating winding 37 of one.coil set .is shown wound about a smaller sup plementary winding 38 ofthe other coil set. These coils are on a bobbin 39 that has one endabutting the plate 33, and its opposite end encircled by a non-magneticassembly plate 40 that is drawn inwardly against the bobbin 39 by anon-magnetic assembly bolt 41. The bolt 41 extends through the plate 33to a threaded engagement with a second non-magnetic assembly plate 42which secures the coil assembly 36 in place. The assembly plates 40, 42also retain a second set of bobbin assemblies 43, 44 that are associatedwith and encircle an upper reed switch (not shown).

In some installations it may be desirable to extend the ferro-magneticpath of the magnetic plate 11, or 33, around the outer sides of the coilassemblies, and such an arrangement is shown in the lower part of FIG. 5for the lowermost reed switch (not shown) that is encircled by a pair ofcoil assemblies 45 and 46. A pair of magnetic tie rods 47 and 48 whichpass through the magnetic plate 43 extend alongside the coil assemblies45, 46. These rods 47, 48 tie together magnetic end plates 49 and 50,which encircle the outer ends of the coil assemblies 45, 46, and theyare also encircled by magnetic tubes 51-54 which are held in tightabutting relation with the plates 49, 50 and the plate 33. Thus, theplates 49, 50 and the tubes 51-54, together with the rods 47, 48 formmagnetic circuits that extend from the flux diverting plate 33 aroundthe outside of the operating coils to provide flux return paths bridgingthe ends of the individual reeds. In this modification stray air flux isgreatly reduced so that magnetic interference between adjacent switchesis correspondingly minimized. Compact assemblies can then be madewithout endangering reliability of performanoe.

When flux is established in a reed by an associated operating coilencircling such reed, the flux that leaks off the reed from near or atthe contact end of the reed must extend back, around the coil to theopposite end of the reed. The plate 11 forms a segment of a path forthis flux, which flux would otherwise be solely air flux. The lowreluctance of the plate 11 modifies the pattern of the return flux bydiverting substantial flux to the plate 11, and this flux divertingproperty of the plate 11 functions to affect the leakage flux leavingthe reed. The effect upon the leakage field, then, is to reduce theworking flux between the reed contact ends when one coil is energized,to thereby preclude switch closure.

The plate 11 must be of sufficient thickness, and the opening 10 musthave small enough diameter, to divert enough leakage flux tosufficiently reduce the net closing forces acting upon the reeds. Forgeneral design purposes the plate 11 should be dimensioned to havesufficient diverting properties for ampere-turn values greater than anyanticipated overload, but this is no particular design problem sinceadequate diversion is readily obtained for ampere-turn values reachingthe physical limit of the coils. As an example, for a readily available0.2 inch diameter reed switch having a contact overlap of .05 inch, aplate inch thick will provide good performance for the coil arrangementsof FIGS. 1 and 4. It can be generalized for these arrangements that thewidth of the magnetic flux diverting member should be at least as greatas the overlap of the reed contact ends. For the embodiment of FIG. 3utilizing latching magnets the flux diverting plate should be ofincreased thickness, and it has been found that a 4 inch thickness givesgood results for a 0.2 inch diameter reed switch.

It is desirable to proportion each operating coil to develop amagnetizing force that substantially saturates the associated reed whendrawing rated current, and economical use of both the coil and reedmaterials may then be achieved. The reeds may also be designed tomagnetically saturate with a small increase of ampere-turns over thatwhich is sufiicient for closure. Then, increased excitation of the coilwill not produce large increments of flux at the reed contact ends, sothe flux diverting plate is not called upon to handle excessive amountsof flux under overload conditions of the coil and the flux through thecontact ends to cause contact closure will not increase markedly.

For the device of FIG. 4 the smaller supplementary coils may be placedinside the main coils, as shown for coils 37 and 38 in FIG. 5, or theymay be placed toward the center of the envelope 1, as schematicallyindicated in FIG. 4. Their modifications of the magnetic field may thenaffect switch operation while remaining at a number of turnssubstantially less than the number of main coil turns. For theconcentric arrangement of FIG. 5 a ratio of from two to one to four toone for the main coil turns to the supplementary coil turns has beenfound satisfactory for usual operation, and the axially inner ends ofthe coils should be set back from the flux diverting plate for aboutinch for a reed switch of the above discussed dimensions.

In summary, the invention provides a reed switch control, in which twosignals are required for initial switch operation, making novel use of afiuX diverting member positioned at the reed contacts to modify themagnetic field, and this in turn provides for elimination of criticaloperating limitations. Further, supplementary coils can be employed toinsure proper opening action for an and logic circuit element.

I claim:

1. In 'a control for a reed switch having a pair of magnetic reeds whichhave relatively movable, facing, normally open contact ends, thecombination comprising: a pair of operating coil means one encirclingeach of the reeds and disposed on opposite sides of the contact ends,each of said coil means establishing magnetic flux in its associatedreed that passes in part across to the other reed to develop anattractive force between the contact ends, which magnetic flux iscumulative with that established by the other coil means, said reedscomprising the dominant magnetic flux paths of magnetic material throughthe centers of said coil means; flux diverting means disposed closelyadjacent to the contact ends between the coil means that provide aregion of low reluctance in the path of magnetic flux branching from thereeds in the vicinity of the contact ends; and latching magnet meansdisposed near the contact ends to establish magnetic'fiux that developsan attractive force between the contact ends that is cumulative with theforces established by the coil means and that is insulficient to movethe contact ends to closed position when neither coil means has beenenergized but is sufficient to hold the contact ends against moving fromclosed position to open position, said flux diverting means divertingflux from passing from one reed contact end to the other uponenergization of one coil means to tend to prevent contact closure, thediversion being such that the ratio of ampereturns necessary for contactclosure when only one coil means is energized to ampere-turns necessaryfor each coil means for closure when both coil means are energized atsubstantially similar levels is at least approximately 3 to 1.

2. In a control for a reed switch having a pair of magnetic reeds whichhave relatively movable, facing, normally open contact ends, thecombination comprising: a pair of operating coil means, one encirclingeach of the reeds, disposed on opposite sides of the contact ends, eachof said coil means establishing magnetic flux in its associated reedthat passes in part across to the other reed to develop an attractiveforce between the contact ends, which magnetic flux is cumulative withthat established by the other coil means, said reeds comprising thedominant magnetic flux paths of magnetic material through the centers ofsaid coil means; flux diverting means disposed closely adjacent to thecontact ends between the coil means that provide a region of lowreluctance in the path of magnetic flux branching from the reeds in thevicinity of the contact ends; and permanent latching magnet meanscomprising at least two magnets disposed between the coil means and onopposite sides of said flux diverting means, with opposite poles facingthe flux diverting means, said means establishing magnetic 'flux thatdevelops an attractive force between the contact ends that is cumulativewith the forces established by the coil means and that is insufficientto move the contact ends to closed position when neither coil means hasbeen energized but is sufiicient to hold the contact ends against movingfrom closed position to open position, said flux diverting meansdiverting flux from passing from one reed contact end to the other uponenergization of only one coil means to tend to prevent contact closure,the diversion being such that the ratio of ampere-turns necessary forclosure upon energization of one coil means to the ampere-turnsnecessary for each coil means for closure when both coil means areenergized at substantially similar levels is at least approximately 3 tol.

3. In a control for a reed switch having a pair of magnetic reeds whichhave relatively movable, facing, normally open contact ends, thecombination comprising: a pair of operating coil means one encirclingeach of the reeds and disposed on opposite sides of the contact ends,each of said coil means establishing magnetic flux in its associatedreeds that passes in part across to the other reed to develop anattractive force between the contact ends, which magnetic flux iscumulative with that established by the other coil means, said reedscomprising the dominant magnetic flux paths of magnetic material throughthe centers of said coil means; flux diverting means disposed closelyadjacent tothe contact ends between the coil means that provide a regionof low reluctance in the path of magnetic flux branching from the reedsin the vicinity of the contact ends; and latching magnetic means with abiasing flux disposed near the contact ends to establish magnetic fluxthat develops an attractive force between the contact ends that iscumulative with the forces established by the coil means and that isinsufficient .to move the contact ends to closed position when neithercoil means has been energized but 'is suflicientto hold the contact endsagainst moving from closed position to open position, said fluxdiverting means diverting flux from passing from one reed contact end tothe other upon energization of one coil means to tend to prevent contactclosure, said flux diversion and said biasing flux being such that theratio of ampere-turns necessary for contact closure when only one coilmeans is energized to ampere-turns necessary for each coil means forclosure when both coil means are energized at substantially similarlevels is at least approximately 3 to 1.

References Cited by the Examiner UNITED STATES PATENTS 2,187,115 1/40Ellwood et al 20087 3,008,020 11/61 Mason '200'87 3,061,696 10/62 .Peek'20093 3,070,677 12/62 Lowry 20087 3,075,059 1/ 63 Blaha et al 200-873,114,008 12/ 63 Petersen et al '20087 3,141,079 7/64 Lowry 20087BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

1. IN A CONTROL FOR A REED SWITCH HAVING A PAIR OF MEGNETIC REED WHICHHAVE RELATIVELY MOVABLE, FACING, NORMALLY OPEN CONTACT ENDS, THECOMBINATION COMPRISING: A PAIR OF OPERATING COIL MEANS ONE ENCIRCLINGEACH OF THE REEDS AND DISPOSED ON OPPOSITE SIDES OF THE CONTACT ENDS,EACH OF SAID COIL MEANS ESTABLISHING MAGNETIC FLUX IN ITS ASSOCIATEDREED THAT PASSES IN PART ACROSS TO THE OTHER REED TO DEVELOP ANATTRACTIVE FORCE BETWEEN THE CONTACT ENDS, WHICH MAGNETIC FLUX INCUMULATIVE WITH THAT ESTABLISHED BY THE OTHER COIL MEANS, SAID REEDSCOMPRISING THE DOMINANT MAGNETIC FLUX PATHS OF MAGNETIC MATERIAL THROUGHTHE CENTERS OF SIAD COIL MEANS; FLUX DIVERTING MEANS DISPOSED CLOSELYADJACENT TO THE CONTACT ENDS BETWEEN THE COIL MEANS THAT PROVIDE TOREGION OF LOW RELUCTANCE IN THE PATHER OF MAGNETIC FLUX BRANCHING FROMTHE REEDS IN THE VICINTITY OF THE CONTACT ENDS; AND LATCHING MAGNETMEANS DISPOSED NEAR THE CONTACT ENDS TO ESTABLISH MAGNETIC FLUX THATDEVELOPS AN ATTRACTIVE FORCE BETWEEN THE CONTACT END THAT IS CUMULATIVEWITH THE FORCES ESTABLISHED BY THE COIL MEANS AND THAT IS INSUFFICIENTTO MOVE THE CONTACT ENDS TO CLOSED POSITION WHEN NEITHER COIL MEANS HASBEEN ENERGIZED BUT IS SUFFICIENT TO HOLD THE CONTACT ENDS AGAINST MOVINGFROM CLOSED POSITION TO OPEN POSITION, SAID FLUX DIVERTING MEANSDIVERTING FLUX FROM PASSING FROM ONE REED CONTACT END TO THE OTHER UPONENERGIZATION OF ONE COIL MEANS TO TEND TO PREVENT CONTACT CLOSURE, THEDIVERSION BEING SUCH THAT THE RATIO OF AMPERETURNS NECESSARY FOR CONTACTCLOSURE WHEN ONLY ONE COIL MEANS IS ENERGIZED TO AMPERE-TURNS NECESSARYFOR EACH COIL MEANS FOR CLOSURE WHEN BOTH COIL MEANS ARE ENERGIZED ATSUBSTANTIALLY SIMILAR LEVELS IS AT LEAST APPROXIMATELY 3 TO 1.